This Program Project Grant application will test the hypothesis that communication between the stroma tissue-resident cells and infiltrating leukocytes is key to directing lung-specific inflammatory and antiinflammatory responses to infection or injury. We believe that the interplay between these cell populations, mediated by alterations in specific extracellular matrix components, is a critical aspect in the development of the response to challenge. Our overall hypothesis is that changes in local pericellular environments, such as deposition of specific extracellular matrix components or the elaboration of effector molecules, as a consequence of the host response to airway epithelial insults, provide spatial signals for recruitment and activation of leukocytes that ultimately shape the qualitative and quantitative patterns of both the innate and adaptive immune responses. An important, unifying, and novel concept that will be explored in this Program is that the progression from innate to adaptive immunity in the lung is fluid and mechanistically linked. Once recruited, infiltrated leukocytes induce further changes in local environments, escalating the inflammatory response. The individual projects in this proposal will probe different, yet complementary and sequential processes of this proposed inflammatory cascade. These aspects include: (1) the role of the interstitial matrix components versican and hyaluronan in regulating and shaping the innate response to lung infection (Wight), (2) the role ofthe epithelial-derived cytokine TSLP (thymic stromal lymphopoietin) in coordinating innate and adaptive responses in the lung (Ziegler), (3) the role of stromelysin-2 (MMP-10) in controlling macrophage activation during acute infection and later T cell responses (Parks), and (4) the role of the adaptive immune system, particularly regulatory T cells, in controlling chronic infection in the lung (Campbell). Each of these projects shares the common theme of how effectors molecules made by one cell type control the activity of specific leukocytes and overall this Program will provide an integrated approach for examining pulmonary inflammation.